1. Field of the Invention
This invention relates to electrical energy generation and more specifically to mud activated electrical power generation for a drilling instrument.
2. Description of the Prior Art
Mud energized electrical power generating systems are known in the drilling art. Drill bit direction information, such as azimuth and inclination, are provided by downhole sensors that are located in the vicinity of the drill bit. Several telemetry techniques are presently in use for transmitting this directional information uphole.
The downhole sensors usually require electrical power for their operation and such power typically has been provided by either batteries or mud-driven turbines. Batteries generally have a relatively short life span since known devices are unable to provide sustained power delivery at the high operating temperatures that characterize conventional drilling operations. Thus the batteries require frequent replacement providing corresponding frequent and costly interruptions in drilling operations.
A mud energized system typically includes a turbine coupled to an electrical generator for providing power to the downhole sensor. The turbine, however, is driven by and thus is in contact with the drilling mud. The drilling mud normally contains cuttings, debris and other abrasives which cause rapid deterioration of the turbine blades that come in contact with the mud. In addition, large solid materials carried by the mud frequently impact and thus damage the turbine blades.
Attempts have been made to place filters in the mud path to filter out some of the material from the mud. However such filters are prone to being clogged thus requiring either maintenance or replacement.
The electrical or hydraulic power generator associated with such mud-driven turbines normally must operate in a protected or "clean" and pressure compensated environment. As a result the power generator is generally placed in a compartment isolated from the drilling mud by a rotary type seal. However, due to the debris ladened, abrasive and corrosive nature of the drilling mud, these rotary type seals are prone to rapid deterioration and even frequent failure.